GSFLOW Modeling of the Souhegan River watershed, New Hampshire DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of the Ohio State University By Taewook Kim B.S. Graduate Program in Environmental Science The Ohio State University 2015 Dissertation Committee: Prof. Frank Schwartz, adviser Prof. Gajan Sivandran Prof. Michael Durand Prof. Larry Brown Copyright by Taewook Kim 2015 Abstract Over several decades, hydrologists have worked to develop an integrated view of processes and parameters important in controlling the behavior of water through the land- based portion of the hydrologic cycle. With the development of GSFLOW, a coupled groundwater/surface water model, the USGS has created a capable system for modeling important hydrologic processes at a watershed scale (Markstrom et al., 2008). GSFLOW combines a land-surface model (Precipitation-Runoff Modeling System or PRMS; Leavsley et al., 1983) and MODFLOW. GSFLOW provides the capability for simulating coupled groundwater/surface-water flow by considering overland flow, saturated and unsaturated flow, and flow routing through streams and lakes. The study area for the GSFLOW application is the Souhegan River watershed, New Hampshire. The purpose of running GSFLOW on this basin is to better understand groundwater and surface water interactions, and particularly the conditions that promote flooding. The specific objectives of the study then are i) to develop PRMS, MODFLOW-2005, and GSFLOW models for Souhegan River watershed, ii) to calibrate the model through a trial and error adjustment of model parameters, iii) to analyze the adequacy of existing and easily available data in creating the model, and iv) to understand the conditions that give rise to flooding. ii There are three calibration steps. First, the calibration of PRMS was carried out manually by trial-and-error adjustments to the values of various parameter files. Typically, only one parameter was changed for each model run to make clear how changes in value affected the calibration. The R2 statistic for the best-fit line is 0.79. Second, MODFLOW-2005 was calibrated as steady state, while comparing simulated and observed hydraulic heads. Third, the calibration of GSFLOW was performed last, after the calibration of PRMS and MODFLOW. A simple plot of measured versus observed discharges (not shown) provides an R2 value of 0.83. After calibration of GSFLOW model, validation is performed as the next step in order to demonstrate the predictive ability of the code and to build confidence in its suitability for applications. iii Dedication This document is dedicated to my loving family, my role model Woosik Kim; my strongest supporter Chunhee Choy; and my lovely sister, Ahyoung Kim. My parents, Woosik Kim and Chunhee Choy, have always cared for me and have always told me “I love you son or I believe you, so do not give up”. Also, I dedicate my dissertation to Ahyoung Kim. Although we had many ‘issues’ growing up as siblings, I do NOT doubt that she is the best sister in the whole world. I would also like to dedicate this dissertation to another family, the Naylor’s. They have treated me as a family member since 2005 when I arrived here in the United States as a foreign exchange student. Because of them, I had exciting holidays and other joyful memories through my years here. I cannot express in words my great thanks to the Naylor’s. I’m going to miss them. I also dedicate this work to my friends, whom motivated me each and every day at 8:00am. Thanks to this morning study group, I was able to manage my time wisely, and I finish my dissertation in a timely manner. Lastly, I would like to dedicate this work to my grandmother, who passed away before I started my master’s degree. She was a humble and generous woman, who always taught me to become a noble man. She always worried about me, because I was the only one of her grandsons living abroad. Her will even requested that I should not be told of iv her death because I might lose my focus on studying abroad. After her death, I promised myself that I would finish this dissertation for her. v Acknowledgments I really want to thank my great adviser, Prof. Frank Schwartz, for his help, especially in finishing my master’s degree and this dissertation. He helped me throughout my master’s degree. I would also like to acknowledge the contributions of Dr. YongJe Kim, a research hydrologist in Korea Institute of Geoscience and Mineral Resources. He provided great encouragement to me when I was an undergraduate student at The Ohio State University and inspired me to choose hydrogeology as my field of study. I also thank to Dr. Ganming Liu, who was long suffering in teaching me about the computer codes and my research. Without his kind support, it would have been impossible to work in developing the model of the Souhegan River Watershed. Lastly, I acknowledge the great help from Dr. Sangsuk Lee. He helped with preparation of figures and guidance in the preparation of the dissertation, and provided helpful advice about my future goals. vi Vita May 2008 .......................................................Grand River Academy 2012................................................................B.S. Environmental Science, the Ohio State University Fields of Study Major Field: Environmental Science vii Table of Contents Abstract ............................................................................................................................... ii Dedication .......................................................................................................................... iv Acknowledgments.............................................................................................................. vi Vita .................................................................................................................................... vii Fields of Study .................................................................................................................. vii List of Figures………………………………………….………………………….………x List of Tables ..................................................................................................................... xi CHAPTER 1: Introduction ................................................................................................. 1 1.1 Purpose and Scope .................................................................................................... 4 1.2 Overview of Souhegan River watershed ................................................................... 5 CHAPTER 2: Study Area Characterization ........................................................................ 8 2.1 Climate and Surface Water Monitoring .................................................................... 8 2.2 Topography, Land Use and Land Cover ................................................................. 10 2.3 Regional Geologic Setting ...................................................................................... 12 2.4 Groundwater ............................................................................................................ 13 2.5 Conceptual Hydrologic Souhegan River watershed................................................ 15 CHAPTER 3: Methods ..................................................................................................... 18 3.1 Surface Water Flow Model (PRMS) ....................................................................... 19 3.2 Groundwater Flow Model (MODFLOW-2005) ..................................................... 22 3.3 Design of Coupled Flow Model (GSFLOW) .......................................................... 27 3.4 Integration of PRMS and MODFLOW-2005.......................................................... 28 3.5 Development of Data Sets for the Souhegan River................................................. 29 CHAPTER 4: Results ....................................................................................................... 33 4.1 PRMS and GSFLOW Data ..................................................................................... 33 viii 4.2 MODFLOW Grid Boundary Condition .................................................................. 42 4.3 MODFLOW Data .................................................................................................... 43 4.4 Calibration of the Models ........................................................................................ 46 4.4.1 PRMS................................................................................................................ 47 4.4.2 MODFLOW...................................................................................................... 51 4.4.3 GSFLOW Calibration ....................................................................................... 52 4.5 Validation ................................................................................................................ 53 CHAPTER 5: Analysis and Discussion ............................................................................ 56 5.1 Water Storage in the Souhegan River watershed .................................................... 56 5.2 Fluxes of Water in the Souhegan River watershed ................................................. 57 CHAPTER 6: Summary and Conclusions ........................................................................ 62 References ........................................................................................................................